Search results for " Darwin"

Identification of the ectosymbiotic bacteria of Mixotricha paradoxa involved in movement symbiosis

2003

Mixotricha paradoxa, a trichomonad from the hindgut of the Australian termite Mastotermes darwiniensis Froggatt, is a rare example of a movement symbiosis between eukaryotic and prokaryotic microorganisms. The surface of Mixotricha paradoxa is covered with spirochaetes and a rod-shaped bacterium. The four flagella at the anterior end seem only to alter the direction of movement, while the ectosymbiotic spirochaetes propel the flagellate cells. Based on a 16S rDNA sequence analysis after a semi-specific PCR, and subsequent fluorescence in situ hybridization applying helper oligonucleotides and a denaturing step of the 16S rRNA, three different spirochaete clones could be clearly identified o…

Bacterial Ectosymbionts which Confer Motility: Mixotricha paradoxa from the Intestine of the Australian Termite Mastotermes darwiniensis

2005

Darwinism and the Origin of Life

2012

Abstract Historically, ideas on the origins of life have been mingled with evolutionary explanations. Darwin avoided discussing the origin of the very first species in public although he acknowledged the possibility that life originated by natural causes. Some of his followers adopted this materialistic position and advocated some sort of spontaneous generation in the distant past. Nevertheless, Pasteur’s experiments were a major obstacle for scientific acceptance of the sudden emergence of life. The scientific study of the origin of life, established in the 1920s, required abandoning the idea of a unique chance event and considering a view of life emerging as the result of a long evolution…

Charles Darwin and the Origin of Life

2009

When Charles Darwin published The Origin of Species 150 years ago he consciously avoided discussing the origin of life. However, analysis of some other texts written by Darwin, and of the correspondence he exchanged with friends and colleagues demonstrates that he took for granted the possibility of a natural emergence of the first life forms. As shown by notes from the pages he excised from his private notebooks, as early as 1837 Darwin was convinced that “the intimate relation of Life with laws of chemical combination, & the universality of latter render spontaneous generation not improbable”. Like many of his contemporaries, Darwin rejected the idea that putrefaction of preexisting organ…

Darwin et l'après-Darwin : une histoire de l'hypothèse de sélection dans la théorie de l'évolution

1992

Les historiens et les biologistes n'ont pas assez distingué la théorie et l'hypothèse de sélection naturelle. En tant que théorie générale de l'histoire de la vie, la doctrine de la sélection naturelle a sans aucun doute eu un immense retentissement dans la science et dans la culture de son temps. Mais l'hypothèse centrale de cette théorie, dans la forme très contraignante que lui avait donnée Darwin, s'est trouvée très vite exposée à des difficultés internes suffisamment redoutables pour entrer en crise à peine était-elle née. En liant rigidement l'hypothèse de sélection à l'hérédité, Darwin l'a exposée pour au moins cinquante ans à la menace permanente d'une réfutation. La sélection darwi…

Les Irlandais : le maillon manquant de la chaîne de l'évolution ?

2011

International audience; L’historien Lewis Perry Curtis ouvrit un large champ de recherche en publiant Apes and Angels en 1971, à un moment où la situation en Irlande du Nord se tendait.

Distinct bhaplotype structure at the innate immune receptor Toll-like receptor 2 across bank vole populations and lineages in Europe

2015

Abstract: Parasite-mediated selection may contribute to the maintenance of genetic variation at host immune genes over long time scales. To date, the best evidence for the long-term maintenance of immunogenetic variation in natural populations comes from studies on the major histocompatibility complex (MHC) genes, whereas evidence for such processes from other immune genes remains scarce. In the present study, we show that, despite pronounced population differentiation and the occurrence of numerous private alleles within populations, the innate immune gene Toll-like receptor 2 (TLR2) displays a distinct haplotype structure in 21 bank vole (Myodes glareolus) populations across Europe. Haplo…

Differential enumeration and in situ localization of microorganisms in the hindgut of the lower termite Mastotermes darwiniensis by hybridization wit…

1999

We examined the abundance and spatial distribution of major phylogenetic groups of the domain Bacteria in hindguts of the Australian lower termite Mastotermes darwiniensis by using in situ hybridization with group-specific, fluorescently labeled, rRNA-targeted oligonucleotide probes. Between 32.0 +/- 7.2% and 52.3 +/- 8.2% of the DAPI-stained cells in different hindgut fractions were detected with probe EUB338, specific for members of the domain Bacteria. About 85% of the prokaryotic cells were associated with the flagellates of the thin-walled anterior region (P3a) and the thick wall of the posterior region (P3b/P4) of the hindgut, as shown by DAPI staining. At most, half of the EUB338-det…

The fine structure of colleterial glands in two cockroaches and three termites, including a detailed study of Cryptocercus punctulatus (Blattaria, Cr…

2007

1873-5495 (Electronic) Journal Article Research Support, U.S. Gov't, Non-P.H.S.; The colleterial glands of insects are organs associated with the female genital apparatus. In cockroaches, these glands produce secretions that cover two parallel rows of eggs during oviposition, and in oviparous species, these secretions become the tanned, sculpted, rigid outer casing of the ootheca. The goal of this study was to compare the gross anatomy of the colleterial glands and the ultrastructure of their component tubules in the phylogenetically significant genera Cryptocercus (Blattaria) and Mastotermes (Isoptera). Recent studies indicate that cockroaches in the genus Cryptocercus are the sister group…

Viatgers romàntics. Els viatges d’Alexander von Humboldt i de Charles Darwin

2013

Tot i pertànyer a generacions diferents i representar formes diferents d’aproximació a l’estudi de la natura, Humboldt i Darwin comparteixen el fet de tenir en l’aventura individual d’un gran viatge iniciàtic la fita determinant de la seva fructífera carrera científica.